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Nuclear Engineering and Design 254 (2013) 129– 141

Contents lists available at SciVerse ScienceDirect

Nuclear Engineering and Design

j ourna l ho me page: www.elsev ier .com/ locate /nucengdes

new design concept for offshore nuclear power plants with enhanced safetyeatures

ihwan Leea, Kang-Heon Leea, Jeong Ik Leeb, Yong Hoon Jeongb, Phill-Seung Leea,∗

Division of Ocean Systems Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of KoreaDepartment of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea

i g h l i g h t s

A new design concept for offshorenuclear power plants is proposed.The total general arrangement for theconcept is suggested.A new emergency passive contain-ment cooling system (EPCCS) isproposed.A new emergency passive reactor-vessel cooling system (EPRVCS) isproposed.Safety features against earthquakes,tsunamis, and storms are discussed.

g r a p h i c a l a b s t r a c t

r t i c l e i n f o

rticle history:eceived 12 June 2012eceived in revised form7 September 2012ccepted 30 September 2012

a b s t r a c t

In this paper, we present a new concept for offshore nuclear power plants (ONPP) with enhanced safetyfeatures. The design concept of a nuclear power plant (NPP) mounted on gravity-based structures (GBSs),which are widely used offshore structures, is proposed first. To demonstrate the feasibility of the concept,a large-scale land-based nuclear power plant model APR1400, which is the most recent NPP model inthe Republic of Korea, is mounted on a GBS while minimizing modification to the original features ofAPR1400. A new total general arrangement (GA) and basic design principles are proposed and can bedirectly applied to any existing land based large scale NPPs. The proposed concept will enhance the

safety of a NPP due to several aspects. A new emergency passive containment cooling system (EPCCS) andemergency passive reactor-vessel cooling system (EPRVCS) are proposed; their features of using seawateras coolant and safety features against earthquakes, Tsunamis, storms, and marine collisions are alsodescribed. We believe that the proposed offshore nuclear power plant is more robust than conventionalland-based nuclear power plants and it has strong potential to provide great opportunities in nuclear

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power industries by deco

. Introduction

On March 11, 2011, an earthquake categorized as 9.0 MW onhe moment magnitude scale occurred off the northeast coast of

apan and a Tsunami struck the northeast shore after the earth-uake. Resulting from these natural events, the Fukushima Daiichiuclear disaster occurred, alerting society to the risks of nuclear

∗ Corresponding author. Tel.: +82 42 350 1512; fax: +82 42 350 1510.E-mail address: phillseung@kaist.edu (P.S. Lee).

029-5493/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.nucengdes.2012.09.011

g the site of construction and that of installation.© 2012 Elsevier B.V. All rights reserved.

power plants again (Hirose, 2012). Even though nuclear powerplants have catastrophic risks, they cannot be abandoned from thecurrent energy portfolio because nuclear power has the smallestcarbon footprint throughout the lifecycle among all energy sourcesand is one of the cheapest available energy sources. Therefore, inorder to use nuclear power continuously and safely, technologydevelopment for enhanced safety is essential for future nuclear

power plants.

One potential solution for using nuclear power safely couldinvolve moving the conventional nuclear power plant (NPP) fromland to ocean in an effort to enhance safety. Generally, this type

1 ng and Design 254 (2013) 129– 141

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Table 1Advantages and disadvantages of three types of ONPP.

(a) Floating typeAdvantages - Transportable and moveable

- Free from the limitation of water depth- Relatively cost effective compared with GBS

Disadvantages - Easily affected by ocean environment- Require tranquil sea areas

(b) GBS typeAdvantages - Transportable

- Provides a land-like condition for topsidefacilities

- High structural safety- Possible to mount very heavy topside plants

Disadvantages - Limitation of water depth (not a good solution indeep sea)

- Lower cost effectiveness

(c) Submerged typeAdvantages - Transportable

- Relatively free from the limitation of water depth- Invisible

Disadvantages - Requires a pressure vessel as a containingstructure

- Difficult to control and maintain the entiresystem

- Requires relatively long and expensive cabling

30 K. Lee et al. / Nuclear Engineeri

f nuclear power plant is called an offshore nuclear power plantONPP). ONPPs have several advantages:

ONPPs are transportable and moveable. This valuable featurecould result in higher fabrication quality and shorter constructionperiods.Since ONPPs can be located farther from residential areas thanconventional land-based NPPs, they may have a positive influenceon the public acceptance of NPPs.ONPPs have ample cooling water using the seawater on whichthey are located. Therefore, sufficient cooling water can be usedif a beyond design basis accident occurs, such as the Fukushimadisaster.The offshore solution may also be attractive with regard to thefuture expansion that can be achieved through allocation of spaceon the first development or by adding other structures or facilitiesthat may be installed adjacent to the existing facilities, withoutconcern for acquiring land or receiving negative public feedback.

Based on the strengths summarized above, many countries haveeveloped concepts and ideas of ONPPs previously, and ONPPesearch continues now. At the beginning of the 1950s, the USAnd USSR began to develop floating nuclear power plants (FNPPs).ecently, Russia’s first floating NPP was scheduled to be completednd is expected to be operational in 2013 (KLT-40s) (IAEA, 2011);urthermore, a submerged NPP concept (e.g. FLEXBLUE) has beenroposed. The submerged NPP could be located offshore to deliverlectricity to a large city near the coastline and is one example of theirection where the nuclear industry is moving to. Russia’s floatingPP uses two 35 MWe reactors derived from those used in Russian

cebreakers. Since the floating type NPP is easily affected by severecean environments, it should be operated in a calm sea area, suchs a port inside breakwater barriers. The undersea ONPP can havehortcomings from the perspective of control and maintenance.oth types of ONPPs can mount nuclear reactors with relativelymall capacity due to the space limitation on the platform.

The key idea of this study is that we adopt gravity-based struc-ures (GBSs) for ONPPs, which have been widely used for manyffshore plants (Lee et al., 2011). GBSs are typically made from steeleinforced concrete in dry docks and tugged to the destination sitefter being floated; that is, GBSs are transportable (Gerwick, 2007).uring operation, they sit on the seabed and bear all the external

oadings by their own weight (gravity). A common GBS applications offshore oil platforms, but recently GBSs are also being used for

ind turbines and LNG terminals. The advantages and disadvan-ages of floating, GBS type, and submerged ONPPs are summarizedn Table 1. It is important to note that, being different from float-ng and submerged NPPs, a GBS can mount large-scale NPPs androvide land-like environments for topside facilities. This paperresents the concept and key ideas of a GBS type ONPP in detail.

To demonstrate the proposed concept, the Advanced Powereactor 1400 (APR1400) developed by the Korea Hydro & Nuclearower (KHNP) consortium was chosen as the NPP model for theNPP; this NPP design is the latest design that has been certifiedy the Korean nuclear regulatory body and is also under con-truction in multiple sites (Korea Hydro & Nuclear Power Co., Ltd.,008). We suggest the modularization method to properly sepa-ate the nuclear power plant facilities into multiple GBS modules,n approach that is typically used for ship fabrication. The estab-ished general arrangement of APR1400 should be revised for theBS type ONPP. Through this work, a new total GA of the GBS typeNPP is developed, and its feasibility and consideration of mutual

hysical connections are also addressed.

To effectively utilize the plentiful source of cooling water fromhe ocean, new concepts for the emergency passive cooling systemEPCS) are suggested: an emergency passive containment cooling

systems to land- Relatively small electricity generation capacity

system (EPCCS) and an emergency passive reactor-vessel coolingsystem (EPRVCS). The EPCCS and EPRVCS use the natural differen-tial head pressure between ballast compartments filled with ballastwater and the inside of the containment as a driving force to oper-ate both systems passively. In addition, a general discussion of thesafety features of the GBS type ONPP against Tsunamis and marinecollisions is presented.

2. Design concept

The GBS is designed as a rectangular structure for ease of con-struction. Instead of developing a new design for the plant layoutand nuclear reactor systems, the existing plant layout and systemof the land-based NPP APR1400 are used. However, the total GAof the APR1400 must be appropriately modified because the entireplant building, site facilities, and other systems need to be sepa-rated and mounted onto GBS modules. To do this, modularizationof the APR1400 components involving the site facilities is proposedwith consideration of the functions of the buildings and facilitiesand systematic correlation from the dual viewpoint of structuraland systematic approaches. In this section, based on the governingdesign parameters, we describe the key concept, a new total GA,and concept design of the GBS type ONPP. However, we wish tostress that the developed ideas in the following sections are notlimited to the APR1400 design, but can be generally applied to anyexisting land based large scale NPPs.

2.1. Design requirements and governing design parameters

Recently, several specific guidelines from certifying companiesthat relate to offshore floating and GBS production have beenissued (Waagaard, 2004); furthermore, the regulatory frameworkand design requirements for nuclear power plants have also been

comprehensively developed. Thus, in order to develop the GBStype ONPP, the design requirements must be satisfied and sev-eral specific guidelines must be followed for both nuclear powerplants and offshore structures. However, for the present phase, the

K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141 131

Table 2Design requirements and parameters of ONPP.

Requirements Parameters

Common with NPP (APR1400) Radiation protection Nuclear/non-nuclear areaSafety requirements (internal) Core damage frequency, containment failure frequency,

occupation radiation exposure, turbine missile strike areaSafety requirements (external) Seismic, Tsunami, storm, aircraft collisionConstruction period and simplicity Modularization of facilities

Special for ONPP Movable and transportable in offshore GBS hull designDraft limitations, ballasting system

Accessibility and refueling in offshore Ocean transportation (ship, helicopter, boat)Settle on sea floor Seabed condition, balanced weight distribution, seabed

foundation designCompact total general arrangement Volume and area of the NPP building and facilities

Physical and functional connection between buildingsExisting offshore facilities, water depth, current drift, weatherconditionFlooding, ship collision, corrosion, run up wave (green water)

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esign requirements and regulations cannot be precisely met andollowed because specific design requirements and regulations forPPs mounted on GBSs have yet to be established; furthermore,revious studies do not exist for GBS type ONPPs. Thus, in this study,

nstead of attempting to satisfy both offshore structure and NPPegulations and guidelines, the focus has been on the common andssential design requirements of the GBS type ONPP. Therefore, inhe conceptual phase, the key design parameters of the GBS typeNPP are proposed based on the established material (Haug et al.,003) and the design requirements, which are described in Table 2.

Generally, the soil conditions and water depth are the dominantarameters for the construction and installation of GBSs. Since theotal weight of the NPP’s main buildings and systems are relatively

assive compared to other facilities, a weight-balanced arrange-ent of the buildings is required to prevent differential settlement

nd the selection of a construction site demands great caution.o avoid blending of the intake and discharge of cooling water,nd prior to fixing the installation direction of the GBS type ONPP,esearch on the current drift is essential and must be reflected inhe design parameters.

.2. Key concept

The GBS is a support structure that retains its position byassive self-weight; GBSs are usually used as an offshore oil plat-

orm and foundation structures in the ocean and are constructedsing steel reinforced concrete. The concrete material has favor-ble characteristics related to fire resistance, radiation shieldingbility, durability against external impact loading but special cares required to waterproof it and protect it against related corrosionroblems, which can be done using pre- and post-tensioning tech-iques, coated reinforcing bars, and special additives in the cementixtures (Gerwick, 2007). Recently, GBSs are also being used for

ffshore wind power plants. A recent example of a GBS offshoretructure is the Adriatic LNG Terminal (Ludescher et al., 2011). Therst offshore liquefied natural gas (LNG) terminal using a concreteBS was successfully fabricated and located 15 km off the Italianoast in September 2008.

The key concept of the GBS type ONPP is the use of the GBS as container and support structure, similar to that used in the Adri-tic LNG Terminal, and the use of a modular design, as employedn ship fabrication, at an on-site factory facility. When the fabrica-ion and assembly of the GBS and NPP components are completed,he GBS modules are launched and towed by tugboats to the ONPP

ite; the modules are then placed on the seabed at the target sitesing a ballasting system. Finally, the GBS modules are rigidly con-ected using steel bars, post-tensioning steel cables, and cementaste (Gerwick, 2007). Then, the GBS modules act as a single rigid

Fig. 1. Key concept of the GBS type ONPP.

structure, thus mitigating the risks related to pipelines and cables.The detailed procedures are shown in Fig. 1 (Lee et al., 2011). Thefour basic steps of this procedure are listed below:

Step 1 A GBS is constructed in a dry dock, fabricated componentsof the NPP are assembled, and the ocean site is prepared inparallel.

Step 2 NPP modules (assemblages of NPP components) aremounted on the GBS. In this step, the first inspections andtesting of the modularized facilities are required prior tolaunching.

132 K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141

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ig. 2. Building components, facilities and pipeline arrangements of APR1400.

tep 3 The GBS based ONPP is floated and towed to the ocean siteby tugboats. At the ocean site, the structure is settled on theseabed using a ballasting system.

tep 4 Nuclear fuel loading and system testing procedures areimplemented by additional construction of the top-sidefacilities. Finally, the GBS based ONPP is ready to supplyelectricity to land after finishing all tests.

.3. New total general arrangement

Previous studies on the modularization of a land-based NPP haveeen carried out in efforts to increase the quality and reduce theosts of future plants. Such research primarily focused on nuclear-elated buildings and their associated systems (Lapp and Golay,997). However, in the present study, with the purpose of prop-rly separating overall buildings and facilities of APR1400 into theeveral GBS modules, the modularization method is used not onlyor the reactor and auxiliary buildings, but also for the overall land-ased NPP site facilities and buildings.

The modularization design method is not discussed in this studyecause the purpose of this study is to propose a new conceptesign of a GBS type ONPP. This paper is the first study to com-ine the fields of offshore structures and nuclear power plants,nd as such it is difficult to follow and apply specific regulationsnd requirements; furthermore, as mentioned in the previous sec-ion, the GBS type ONPP is developed based on the land-based NPPPR1400. Thus, the established GA of the APR1400 is used, particu-

arly for the nuclear-related buildings and their associated systems.lso, the APR1400 is the most recently certified Korean NPP model,nd the nuclear-related buildings and their associated systems arelready modularized. In this paper, the meaning of modularizationorresponds to all NPP buildings and site facilities. The APR1400 GAnd pipeline arrangements are shown in Fig. 2 and the correspond-ng legend is given in Appendix A.

In order to modularize the land-based NPP (APR1400) model,

he design factors must be examined thoroughly; the design factorsnclude the physical connectivity, nuclear and non-nuclear build-ngs, pipeline arrangement, building weight, building placementymmetry, and availability of fabrication and maintenance. The

Fig. 3. New total GA of the GBS type ONPP with differentiation of the nuclear andnon-nuclear areas.

new total GA should be developed considering these design factors.In this study, the meaning of the new total GA is not limited to theturbine building, compound building, reactor containment build-ing, and reactor auxiliary building; rather, it includes all facilitiesand buildings of the APR1400.

2.3.1. Nuclear and non-nuclear areasBased on the APR1400 GA, a new total GA for the GBS type

ONPP is proposed. First, the APR1400 building components arecategorized into nuclear and non-nuclear buildings. A detailed dif-ferentiation of the nuclear and non-nuclear areas is shown in Fig. 3.The shaded sections indicate the nuclear area and the unshadedsections indicate the non-nuclear area.

The nuclear buildings include the following:

- Reactor containment building- Reactor auxiliary building- Waste process building- Fuel handling building

The non-nuclear buildings include the following:

- Turbine generator building- Intake structure- Control building- Compound building- Water treatment building- Accommodations and other warehouse buildings

2.3.2. Modularization of the NPP buildings and facilitiesBased on the APR1400 GA and the nuclear and non-nuclear area

categories, the element groups are suggested and a new total GAfor the GBS type ONPP is developed. Before modularizing the totalNPP components, the building functions and NPP system assign-ments must be considered. The GBS type ONPP consists of threeGBS modules and each module is composed of up to six elementgroups (with a total of eight different groups; some groups areduplicated). Fig. 3 shows the arrangement of the three modulesand fifteen components. The details and functions of each groupare as follows.

(1) Group 1 includes the following elements:

- AAC D/G building- Auxiliary boiler building- Auxiliary boiler fuel oil storage tank- Fresh water storage

K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141 133

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ig. 4. Layout of the turbine and reactor buildings of (a) APR1400 and (b) ONPP inrder to protect the reactor building from a turbine missile strike.

This group has no direct correlation with the reactor build-ing and safety systems and also contains flammable facilities,materials, and fresh water storage. It must remain apart fromthe reactor building systems.

2) Group 2 includes the following elements:- Turbine generator building- Main transformer- Standby auxiliary transformer- Unit auxiliary transformer- Spare main transformer- Lube oil storage tank and centrifuge house

When the over-speed protection system of a turbine blademalfunctions, missiles resulting from destructive over-speedfailures are typically generated. During such failures, the mis-siles can cause serious damage to even substantially reinforcedconcrete slabs and walls of reactor buildings. Therefore, tur-bine missile strikes must be considered, as shown in Fig. 4(a),according to the regulatory guidelines regarding protectionagainst low-trajectory turbine missiles as formulated by theU.S. Nuclear Regulatory Commission (U.S. NRC, 1977). In thecase of the ONPP shown in Fig. 4(b), the turbine missile strikezone is bounded within each GBS module due to the additionalconcrete walls of GBS hulls, which do not exist in the APR1400design. The electric power systems are correlated with the tur-bine generator building; thus, the main, standby, and sparetransformer and switchgear buildings must be located in thesame group.

3) Group 3 includes the following elements:

- Reactor make up water tank- Hold-up volume tank- Boric acid storage tank

Fig. 5. Layout of the auxiliary building and reactor containment building.

The reactor make-up water system and hold-up volume tankmust be located next to the reactor building systems becausethese facilities have heavy physical connections with the reac-tor building systems.

(4) Group 4 includes the following elements:- Reactor containment building- Auxiliary buildings

The auxiliary buildings are designed as a quadrant shape,allowing them to wrap around the containment building anddivide the safety systems into four sections, as shown in Fig. 5.Through the quadrant shape safety systems, the auxiliary build-ings are able to manage conflagration, flooding, and otherexternal accidents.

(5) Group 5 includes the following elements:- Office building- Compound building- Control building

For the convenience of controlling and operating the ONPP,the office building and control building are positioned at thecenter of GBS Module 2.

(6) Group 6 includes the discharge pond and facilities.The discharge pond is located next to the water treatment

systems, allowing easy drainage of the water from the ONPPand also avoiding interference with the intake structure. Thedischarge pond and facilities must be located far from the intakestructure and should have a different emission direction to thatof the water intake direction.

(7) Group 7 includes the following elements:- Wastewater treatment facility- Fire pump and water/wastewater treatment building- Caustic and acid storage tank- Cooling tower- Chlorination building- Sodium hypochlorite holding tank

In order to easily manage the used water and chemical wastethat are generated from the power plant, the sanitary watertreatment facility and wastewater treatment facility shouldhave a physical connection with the reactor building systems.

(8) Group 8 includes the following elements:- Intake structure- Intake reservoir

- CCWHX building- ESW intake structure- Sanitary water treatment facility

134 K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141

Fig. 6. Diagonally symmetric arrangement of groups considering weight balance.

Table 3Weight information of APR1400.

Weight (ton)

Reactor building 480,000Auxiliary building 540,000Compound building 76,000Turbine generator building 440,000Other facilities 200,000

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In order to secure and store the circulation cooling water forhe facilities in the ONPP, this subcategory requires sufficient spaceor the reservoir systems and water treatment facilities. The ESWntake structure and CCWHX buildings have physical connections

ith the turbine generator building and reactor building systems,oth directly and indirectly; hence, this subcategory should be con-ected with the turbine generator building. The intake structurend reservoir systems should be connected with the accommoda-ions and office buildings in order to supply potable water to theperators and workers.

.3.3. Symmetric structure arrangement considering the weightalance

In the case of land-based NPPs, the main buildings and facili-ies have independent foundations, but ONPPs share foundationsecause the reactor building, turbine generator building, and otheracilities are mounted onto the same GBS module. Hence, the totaleight balance is a very important design parameter when devel-

ping a new total GA in order to prevent differential settlement.able 3 presents the weight information for APR1400.

For the GBS Module 2, Group (8) is symmetrically located atoth ends and Group (5) is located in the center of GBS Module 2.onsequently, GBS Module 2 has a symmetric arrangement witheight balance. Group (4) and Group (2) are the heaviest compo-ents of GBS Module 1 and GBS Module 3, respectively. Group (4)hould be located at the middle of GBS Modules 1 and 3 because itontains the auxiliary and reactor buildings. If Group (4) is locatedt the identical ends of the GBS module, it could cause differentialettlement. Group (2) is the second heaviest area of GBS Modules

and 3. Unlike Group (4), Group (2) should be placed at the endsf the GBS module, but should be located at opposite ends side ofBS Modules 1 and 3. If Group (2) is placed at the same end of GBS

odules 1 and 3, it could cause differential settlement. Thus, the

ew general GA has a diagonally symmetric arrangement and alsohe center of the mass exists on a diagonal axis, as shown in Fig. 6.

Fig. 7. Intake and discharge pipe line arrangement of the GBS type ONPP.

2.3.4. Pipeline arrangementA new total GA for the GBS type ONPP is proposed based on the

design parameters and with feasibility considerations suggestedin the previous section. As the arrangement of the NPP compo-nents is modified for the GBS type ONPP, the pipeline arrangementof APR1400 must also be rearranged according to the new totalGA. The rearranged pipelines are shown in Fig. 7. Compared to thepipeline arrangement of APR1400, the pipeline arrangement for theGBS type ONPP is relatively simpler and the overall pipeline lengthis shorter.

In case of the APR1400, the intake structure and reservoirs arelocated approximately 200 m from the turbine building, and thecooling water discharge pond is located far from the power plantsite in order to prevent mixing of the intake and discharged cool-ing water. Thus, the overall pipeline length is very long. However,since the turbine building group of the GBS type ONPP is locatednext to the intake structure and reservoir group, the intake pipelineis short. Furthermore, because the cooling water discharge pondand turbine building are positioned in the same GBS module, theoverall discharge pipeline length can be reduced. Consequently, theGBS type ONPP is more economical in terms of pipeline length.However, the intake structures and discharge ponds are positionedwithin the GBS type ONPP, and the risk of blending the circulat-ing cooling water is relatively high. In order to prevent mixing ofthe circulating cooling water, the current drift must be consideredprior to determining the installation direction of the GBS. If nec-essary, extension of the discharge pipeline to a location fartheraway or introduction of an additional discharge pond located else-

where can reduce the risk of the circulating cooling water beingmixed.

K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141 135

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Fig. 8. Design and dimensions of a single GBS module.

.4. Concept design

In this section, all main buildings and other facilities of the NPP,s modularized in Section 2.3.2, are arranged with three GBS mod-les based on the considerations explained in Sections 2.1 and 2.3.

The design philosophy of the GBS type ONPP centers on com-actness and safety. Through modularization and rearrangement ofite facilities and pipelines, the total site area of NPP can be reduced.he GBS type ONPP has overall dimensions of 270 m (L), 330 m (W),nd 53 m (H), and each GBS concrete caisson module is 270 m (L),10 m (W), and 53 m (H) with a symmetric arrangement. The orig-

nal site area of APR1400 is 225,000 m2 and the ONPP site area is9,100 m2; the total site area of the GBS type ONPP is thus reducedy 60% (135,000 m2) compared with the original site area.

In order to settle the GBS to the seafloor, use of ballasting andeballasting systems is essential. The GBS has a surrounding con-rete double bottom and concrete double walls and the huge spaceetween the walls can be used for ballasting systems; the doublealls can also increase the durability of the GBS against ship andoating object collisions. The safety features of the GBS type ONPPre demonstrated in Section 3 in more detail.

The target water depth of the GBS type ONPP at the construc-ion site is 30–35 m. The suggested height of the GBS is 53 m inhis study, which allows 18–23 m of freeboard to be secured. The8–23 m of freeboard is sufficient to effectively prevent “greenater” on top of the GBS under storm and severe weather condi-

ions. The detailed dimensions and design of the concrete caissonsre shown in Figs. 8 and 9.

The APR1400 model is composed of two independent reactornits and turbine generator buildings. However, the compound

uilding, intake structure building, and other site facilities arehared by the two reactor units and turbine generator buildings.he GBS type ONPP also has two independent reactor units andurbine generator buildings and shares the compound building,

Fig. 9. Design and dimensions of all GBS modules.

Fig. 10. Assembly of the element groups and GBS Modules 1 and 3.

control building, and accommodations. However, in contradistinc-tion to the APR1400, the GBS type ONPP cannot share its sitefacilities, because each reactor unit and its related facilities are sep-arated into GBS Module 1 and GBS Module 3; thus, the site facilitiesshould accordingly be separated into GBS Module 1 and GBS Mod-ule 3. In general, the site facilities of the NPP are responsible forstoring, monitoring, and supporting the NPP systems. In this study,most site facilities are assigned to Groups (1), (3), and (6). The GBStype ONPP is composed of three GBS modules: GBS Modules 1 and3 contain Groups (1), (2), (3), (4), (6), and (7), but the vertical andhorizontal arrangement directions of GBS Module 3 are opposite tothat of GBS Module 1 to prevent differential settlement due to thesymmetric structure arrangement.

GBS Module 2 is composed of two Group (8) sections and a sin-gle Group (5) section. The two intake structures and facilities arepositioned in GBS Module 2 to supply cooling water to GBS Mod-ules 1 and 3. The main control building and compound buildingsare placed at the center of the GBS type ONPP for convenience ofmaintaining and controlling the entire system. The accommoda-tions and refuge sites should be located as far from the reactor aspossible in order to allow workers to easily escape in an emergency.Therefore, Group (8) is a suitable location for the accommodationsand refuges. The assembly process of GBS Modules 1, 2, and 3 areshown in Figs. 10 and 11, and a side view of each GBS module andits component groups are shown in Figs. 12 and 13. After settlingthe three GBS Modules, the modules are combined as a single struc-ture, as mentioned earlier. The final concept design of the proposed

Fig. 11. Assembly of element groups and GBS Module 2.

136 K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141

Fig. 12. Side view of GBS Module 2: Group (8) and Group (5) are the components of GBS Module 2.

Fig. 13. Side view of GBS Modules 1 and 3: Group (7), Group (4),

Fig. 14. Floor plan of the GBS type ONPP.

and Group (2) are the components of GBS Modules 1 and 3.

3. Safety features

During the past three decades, the largest and most widelyknown nuclear accidents were the Fukushima Daiichi nucleardisaster (2011, Japan), the Chernobyl accident (1986, Ukraine(FSU)), and the Three Mile Island (TMI) nuclear accident (1979,United States). In the Fukushima case, the nuclear disaster resultedprimarily from an earthquake, which collapsed a transmissiontower. With the loss of the off-site power, the emergency powersystem worked normally, but when the Tsunami that resulted fromthe earthquake struck the NPP, the emergency diesel generator(EDG) were submerged and the component cooling system, sea-water pump, and fuel tanks were destroyed. Finally, the ECCS andcirculating cooling system were suspended due to the NPP losingpower.

The TMI accident occurred due to mechanical system failureand worsened by the failure of the plant operators to recognizethe loss of coolant accident. The accident began with failures inthe non-nuclear secondary system, followed by a pilot-operated

relief valve (PORV) being stuck open in the primary system, whichallowed large amounts of the nuclear reactor coolant to escape. Thiscaused a partial meltdown of the reactor core. As demonstratedby these two nuclear accidents, the weak spot of NPPs is that,

K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141 137

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ithout electrical power, a continuous supply of coolant is impossi-le in the event of a major accident and the plants are easily affectedy natural disasters such as earthquakes and Tsunamis. The NPPs

n the future should be immune to any type of anticipated naturalisasters combined with loss of active power supply by providingdequate cooling under given circumstances.

Unlike land-based NPPs, ONPPs have ample cooling waterecause they are surrounded by seawater, and in emergencies, sea-ater can be used as a backup for cooling when the existing active

ystem fails due to unforeseen reasons. That is, the ONPP can obtainoolant supplied passively from the ocean into the reactor contain-ent building using a natural differential head between the ocean

nd inside the reactor containment building in the case of powerutages. In this study, new emergency passive cooling systemsEPCS) that use seawater along with ballast water are suggested.

In addition to securing an ample source of cooling water, the GBSype ONPP has benefits against earthquakes, Tsunamis, storms, and

arine collision impact. We describe the safety features of the GBSype ONPP used to cope with natural disasters and marine accidentsn the following sections.

.1. Emergency passive containment cooling system (EPCCS) andmergency passive reactor-vessel cooling system (EPRVCS)

The APR1400 model has active cooling systems including themergency core cooling system (ECCS), emergency diesel gener-tor (EDG), containment spray system (CSS), in-vessel retentionIVR), and hold-up volume tank (HVT), as shown in Fig. 16. How-ver, during a total station blackout, where both onsite and offsiteower are lost, the above active cooling systems cannot guarantee

ong term cooling, and consequently the risk elevates and a disas-er such as the Fukushima nuclear case can occur. After the TMIuclear accident in 1979, the EPCS was adopted internationally as

design improvement to increase the safety margin and reduce thenvestment risk. The driving forces of the passive system are natu-al phenomena such as pressure and gravity. Therefore, the systems relatively simple and the reliability of operational performances high. Following the Fukushima nuclear disaster, there is grow-ng desire for a passive core cooling system that can remove theesidual heat over a long period.

A good example of a nuclear reactor that has adopted a pas-ive safety system is the AP1000 system designed by WestinghouseUSA). The AP1000 has several passive safety features including aassive core cooling system and passive containment cooling sys-

em. Also, a passive fluidic device is installed at the safety injectionank (SIT) in APR1400 to control the flow without any interven-ions, and another passive system (a passive auxiliary feedwaterystem; PAFS) is now being developed for the APR+ model by Korea

f a GBS-type ONPP.

Hydro & Nuclear Power Co., Ltd. However, these passive systems arebeing developed for land-based NPPs. Thus, in this paper, to sup-plement the established active and passive cooling systems, theEPCCS and EPRVCS are proposed as passive cooling systems for theGBS type ONPP; these passive cooling systems use the natural dif-ferential head between the ballast compartments and inside thecontainment as the driving force of the passive system.

3.1.1. EPCCS conceptDuring certain accident scenarios, pressure can be elevated

gradually in the containment if the containment cooling systemfails. For instance, during a total station black out accident, reduc-ing pressure inside the containment may not be possible with thecurrent APR1400 system design since it relies on the active con-tainment cooling system. In other words, the EPCCS operates whenan accident which occurs is beyond the design basis accident. Asa remedy to this situation, the ONPP can be equipped with a heatexchanger using ballast water as a coolant and operated by thenatural differential head due to steam generation inside the heatexchanger and the water level in the ballast water compartment.The detailed concept of the EPCCS is shown in Fig. 17(a) and thecomponents of the systems are as follows:

• Steam delivery pipeline• Ballast compartment and ballast water• Ballast water pipeline• Heat exchanger• Filtered venting system

A GBS has a ballasting system, and the ballasting compartmentis filled with water or a solid material (e.g. sand); if necessary, bothmaterials can be used. The ballasting tank acts as a condenser and acold water source in case the active containment cooling system isnot available. As shown in Fig. 17(a), a heat exchanger is installedin the containment. The cold water source is supplied from the bal-last water compartment. During an accident, steam is generatedwithin the heat exchanger due to elevated temperature in the con-tainment and the generated steam is delivered to the ballastingcompartments by the steam delivery pipeline. In this system, theballasting compartment acts as a condenser. The ballast water con-stantly circulates in the system to cool down the containment andreduce the pressure to prevent failure of the containment. There-fore, the water in the ballasting tank is the ultimate heat sink forthe EPCCS. However, the amount of ballast water might be insuf-

ficient to continuously supply cold water until the containment issufficiently cooled. Hence, in the design phase, in order to securesufficient ballast water for long term cooling, the size of the bal-lasting cell must be designed to be larger than the other ballasting

138 K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141

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ig. 16. Active cooling system of APR1400 model; emergency core cooling system (Eater storage tank (IRWST), and hold-up volume tank (HVT).

ells. Furthermore, the ballasting cell is connected to the sea via aassive valve, which is called venting system; when the pressurend temperature of the ballasting cell are too high they can beelieved through this safety relief valve.

To cool the containment more efficiently and evenly, installationf multiple heat exchangers is suggested in this paper as depictedn Fig. 17(b). The EPCCS can consist of multiple heat exchangersonnected to several ballasting compartments, because the GBS isurrounded by several ballasting compartments. However, steamenerated from a heat exchanger can obtain radioactive matterven though the heat exchanger physically separates the contain-ent steam–air mixture from ballast water. Therefore, a filtered

enting system is required on the steam delivery pipeline to reducehe risk of uncontrolled radiation release to the environment. Theystem commonly consists of a scrubbing chamber and metal filter.

The purpose of the EPCCS is to cool and decrease the inner pres-ure of the containment to prevent the structural failure of thentire containment system. However, the EPCCS can sufficientlyool the containment but cannot prevent reactor vessel failure if theccident proceeds to a beyond design basis accident when the cores severely damaged, such as in the case of TMI or Fukushima. In theollowing chapter, in order to protect the reactor vessel form fail-ng during a severe accident, an emergency passive reactor-vesselooling system (EPRVCS) is proposed; this system directly cools theeactor vessel using ballast water/seawater.

.1.2. EPRVCS conceptIn contradistinction to the EPCCS, the EPRVCS cools the reactor

essel directly using ballast water/seawater if the accident resultsn severe core damage. In other words, this is a passive in vesseletention (IVR) strategy that utilizes the full potential of the ONPP.n this case, in addition to the EPCCS, after passing through theow pass for passive in-vessel retention, the ballast water is sentirectly to the reactor vessel wall and fills the reactor cavity toxternally protect the reactor vessel from relocated nuclear fuel.he components of the EPRVCS are as follows:

Filtered venting systemBallasting cell and ballast waterFlow path for passive in-vessel retention

ontainment spray system (CSS), in-vessel retention (IVR), in-containment refueling

• Sea pipeline

If melting or significant degradation of the reactor core isexpected or confirmed based on the information available andadequate core cooling is not expected, cooling and in-vessel con-finement of the core melt through external vessel cooling can bepursued. If the pressure in the containment is higher than thehydraulic head, the containment pressure can be balanced by theEPCCS. After securing an adequate hydraulic head, the pressurevalve attached at the end of the passive in-vessel retention lineis opened and the ballast cells’ water continuously flows into thereactor cavity and directly cools the reactor vessel by using the nat-ural differential head between the ballast compartments and theinner of the containment. When the water and reactor vessel comeinto contact, steam is generated in the containment. In this phase,containment is cooled by the EPCCS, which acts as a heat sink, andcondensed steam is stored in the in-containment refueling waterstorage tank (IRWST), as shown in Fig. 17(a).

The EPRVCS uses ballast water to flood the reactor vessel upto the hot legs and cold legs. The steam from produced boil-ing on the reactor vessel surface can be condensed by the EPCCSand returned to the reactor cavity by gravity. Long-term coolingof reactor vessel can be maintained by this natural recirculationof water. By the in-vessel cooling and confinement of the coremelt, a severe accident can be terminated in-vessel and thus thedispersion of fission products in the containment can also be mini-mized. By protecting the reactor and containment using the EPRVCSand EPCCS, respectively, any significant offsite radiological conse-quences such as those experienced in the TMI-2 accident can beprevented.

3.2. Seismic effects

The ballasting compartment is filled with water or heavy solidmaterials to secure sufficient gravity of the GBS; that is, the totalweight of the GBS can be controlled by using the ballasting anddeballasting systems. Under seismic loading, the weight of the

structure is a dominant factor of the dynamic response. By reduc-ing the total weight of the GBS, a seismic isolation effect can beintroduced. Seismic isolation technologies have already long beenapplied to land-based nuclear power plants and other plants.

K. Lee et al. / Nuclear Engineering and Design 254 (2013) 129– 141 139

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Fig. 17. Concept design of the emergency containment cooling system

The principle of the base isolation system is to decouple superstructure from its substructure. Among many possiblease isolation mechanisms, we can effectively use the frictionechanism governed by the friction force between the GBS and

eabed. The friction force is a function of the friction coefficientnd the total weight of the superstructure. Thus, we can controlhe friction coefficient determined by the interface conditions andhe total weight of the GBS type ONPP.

There are two methods to change the total weight of the GBS.he first method is using the ballasting system. By discharging theontained ballast water in the ballasting compartments, the total

eight can be reduced. The second method is attaching a large buoy

o the structure; this method is already used to control the GBSalance in offshore oil platforms. In short, by reducing the totaleight of the GBS, the vertical load acting on the seabed can be

CS) and emergency passive reactor-vessel cooling system (EPRVCS).

reduced, and the friction force at the GBS bottom is then reduced.Consequently, the GBS slides more easily, and in this state it acts asa friction base isolation system. The friction base isolation systemused for the GBS is shown in Fig. 18.

In a normal state, in order to prevent sliding of the GBS mod-ules due to severe wave loads, current and tides or other externalocean environmental loads, sufficient shear resistance at the baseis provided by a corrugated steel skirt driven into the ground. As aminimum skirt height, 2.0 m is recommended (Waagaard, 2004).For the Adriatic LNG Terminal, a 1.0 m corrugated steel skirt isextended into the ground; however, the skirts below the base slab

are usually designed to yield during an extreme earthquake. Fur-thermore, in addition to the base isolation effects, the kinematicenergy of the structures caused by an earthquake can be absorbedby the surrounding seawater, which acts as a natural damper.

140 K. Lee et al. / Nuclear Engineering and

Fig. 18. Base-isolation system of ONPP using the friction mechanism between GBSand seabed.

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Fig. 19. Wave height of Tsunami.

In order to clarify the effects of the base isolation and sea-ater damping, a dynamic response analysis of the GBS during

real earthquake is essential, which includes research into theuid–structure–soil interactions. Such work remains for futuretudy.

.3. Safety against Tsunamis, storms, and marine collisions

Due to the ease of securing the circulating cooling water andhe problem of public acceptance, land-based NPPs have mostlyeen located near the seaside but far from residential areas. Thus,

n the event of a natural disaster such as a Tsunami, NPPs situatedn or near coastlines can be easily damaged, as in the Fukushimauclear disaster.

The main cause of the Fukushima nuclear accident was a powerutage due to the Tsunami inundating the EDG facilities. Tsunamisave water waves with small amplitude and very long wavelength

n the deep sea. However, the wave height rapidly increases to tensf meters when they approach the shoreline, as shown in Fig. 19.y using a shallow water equation and energy flux conservationheorem with the assumption of a long wave, the Tsunami heightan be approximated by the relation between the wave height andater depth:

HA

HB=

(hB

hA

)1/4

(1)

here H and h are the wave height and water depth, respectively,nd the subscripts (A and B) denote two different positions. Accord-ng to the wave height of 6.7 m and water depth of 204 m measuredt 20 km off Fukushima, the calculated Tsunami height would be2 m at the target position of the ONPP with water depth 30 m.he designed 23 m freeboard of the GBS type ONPP is sufficient torevent inundation of the safety systems and facilities mountedn the GBS if a Tsunami in the same class as that of Fukushima

ccurs. These calculated data demonstrate that the GBS type ONPPs relatively safer than land-based NPPs in the event of a Tsunami.

Many shore facilities have been destroyed by collisions of float-ng objects when Tsunamis have occurred. Concrete is a durable

Design 254 (2013) 129– 141

material against impact loads such as marine collisions and the GBSis designed to have concrete double walls. Due to this structural fea-ture, damage to the facilities and systems of the GBS type ONPP willbe significantly minimized in the event of an accident. If one layeris damaged due to a collision or similar accident, the second layeracts as a back-up and prevents the ingress of seawater into the GBS.

While storms are an important threat for floating structures,they do not have a severe influence on the safety of the GBS becausethe GBS is a massive structure that sits on the seabed. However,securing sufficient freeboard from the sea surface requires carefulconsideration in the design phase to avoid ‘green’ water on the GBSdeck due to wave run-up (Van Wijngaarden et al., 2004). As men-tioned earlier, the designed height of the GBS is 53 m and the targetwater depth is 30–35 m. The freeboard of 18–23 m is adequate toprevent ‘green’ water on the GBS deck in the event of storms atmost places.

4. Concluding remarks

The concept design of a GBS type ONPP was developed to sat-isfy the essential design requirements of nuclear power plants thatoperate in the ocean and enhance its inherent safety and increasethe passive safety nature of the nuclear system. In this study, severalgoverning design parameters and considerations were proposedfrom systematic and structural perspectives. Finally, we organizedthe important design parameters and functional requirements ofONPP, as summarized in Table 2, to emphasize further challengespertaining to ONPP.

As the supporting and containing structure for the NPP, grav-ity based structures (GBSs) were chosen due to their features ofdurability, stability, and radiation shielding in ocean environments.To demonstrate the feasibility of the proposed idea, APR1400 wasselected. In order to mount the APR1400 into three GBS modules,a new general arrangement (GA) was developed and a modulardesign method was used to separate the overall facilities of theAPR1400 into GBS modules. Consequently, the total footprint of theGBS type ONPP is reduced by 60% compared to the original NPP.Furthermore, a symmetric arrangement was achieved by consid-ering the total weight balance of the GBS type ONPP to preventdifferential settlement at the seabed. According to the new totalGA, the overall length of the pipelines is reduced and the circulat-ing cooling system is simplified by using seawater as the coolant.By reducing the overall pipeline lengths and simplifying the coolingsystem, economic gains are expected.

To enhance the existing emergency passive cooling system(EPCS) and active containment cooling systems of APR1400, newconcepts for the EPCS were proposed: an emergency passivecontainment cooling system (EPCCS) and an emergency passivereactor-vessel cooling system (EPRVCS). The EPCCS and EPRVCSuse the natural differential pressure head between the ballast com-partment and inside the containment as the driving force for thesystems. For instance, during a total station black out accident, theEPCCS reduces pressure inside the containment by heat exchang-ers, which using ballast water as a cold water source. The ballastwater constantly circulates through the system to cool down thecontainment and reduce the pressure inside it to prevent contain-ment failure. In addition to the EPCCS, the EPRVCS was suggested forthe case of significant degradation of the reactor core. The systemcools and confines the corium in the reactor vessel through exter-nal vessel cooling by ballast water/seawater passive injection to thereactor cavity. The EPRVCS uses ballast water to flood the reactor

vessel up to the hot legs and cold legs. By cooling and confinementof the core melt in the reactor vessel through the EPCCS and EPRVCS,a severe accident can be terminated in vessel and thus the releaseof fission products to the containment can also be minimized.

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K. Lee et al. / Nuclear Engineeri

We discussed the safety features of the GBS type ONPP in thevent of a natural disaster such as an earthquake or Tsunami. Inhe case of an earthquake, according to control of the GBS weight,he GBS bottom is easily decoupled from the seafloor and transfer ofccelerations into the structure can be reduced. The GBS type ONPPs relatively safer than land-based NPPs in the event of a Tsunami.he Tsunami height at the target design water depth (30 m) of theBS is smaller than that at the shoreline. By using a simple equation,e confirmed that the Tsunami height at the GBS would be 12 m

n the case of the Fukushima Tsunami. Therefore, a freeboard of3 m is sufficient. Consequently, the mounted facilities of the GBSype ONPP will be free from green water. Furthermore, for marineollisions, the reinforced concrete double walls of the GBS provideufficient structural safety against the impact load.

In the present study, we suggested the concept design of a GBSype ONPP based on a new total GA and enhanced passive safetyystem concepts: EPCCS and EPRVCS using ballast water/seawaters a coolant. By further developing this concept design, we canxpect safer and continuous utilization of nuclear power in theuture. Further studies are required to examine the seismic per-ormance, the structural safety against Tsunami and storms, theffectiveness of the EPCCS and EPRVCS, and the economic feasibil-ty of the entire system. In addition, nuclear refueling proceduresnd accessible facilities (for example, berthing facilities for shipsnd platforms for helicopters) should be considered.

cknowledgement

This work was supported by a grant from the Human Resourcesevelopment (No. 20114030200040) of the Korea Institute ofnergy Technology Evaluation and Planning (KETEP) funded by theorean Ministry of Knowledge Economy.

ppendix A. The building and facilities legend of APR1400

. Chlorination building

. Sodium hypochlorite holding tank

. CCWHX building

. ESW intake structure

. ESW supply pipe

. ESW discharge pipe

. CW intake structure

. CCW supply and return piping

. N/A0. Lube oil storage tank and centrifuge house1. CO2 storage tank area2. Chemical storage tank area3. Unit auxiliary transformer4. Main transformer5. Standby auxiliary transformer6. Transformer removal rail load7. Spare main transformer8. Condensate storage tank9. N/A0. AAC D/G building1. Reactor make-up water tank2. Hold-up tank3. Boric acid storage tank4. Cold machine shop5. N2 and H2 storage cylinder area6. Fire pump and water/wastewater treatment BLDG7. Caustic and acid storage tank8. Fresh water storage tank9. Demi water storage tank0. Auxiliary boiler BLDG1. Auxiliary boiler fuel oil storage tank2. COND. Tube pull Pit (typ.)

3. GIB tunnel4. CV cable tunnel5. Excitation transformer6. CW intake conduit7. CW discharge conduit

Design 254 (2013) 129– 141 141

38. Underground common tunnel39. Wastewater treatment facility40. Transformer area pump41. Spare transformer42. Cooling tower43. CW discharge pond44. N/A45. N/A46. KHNP’s office area47. Guard house48. Intake reservoir49. Parking area50. Sanitary water treatment facility

Appendix B. Abbreviations

1. ACC D/G: alternative alternating current diesel/generator2. APR1400: Advanced Power Reactor 14003. AUX: auxiliary area4. BLDG: building5. CCW: component cooling water6. CCWHX: component cooling water heat exchanger7. CV: containment vessel8. CW: cooling water9. CSS: containment spray system

10. EDG: emergency diesel generator11. EPCCS: emergency passive containment cooling system12. EPCS: emergency passive cooling system13. EPRVCS: emergency passive reactor-vessel cooling system14. ESW: emergency service water15. FNPPs: floating nuclear power plants16. GA: general arrangement17. GBSs: gravity based structures18. GIB: gas insulated bus19. HVT: hold-up volume tank20. IRWST: in-containment refueling water storage tank21. IVR: in vessel retention22. KHNP: Korea Hydro & Nuclear Power23. LNG: liquefied natural gas24. NPP: nuclear power plant25. ONPP: offshore nuclear power plant26. PAFS: passive auxiliary feedwater system27. PORV: pilot operated relief valve28. SIT: safety injection tank29. TMI: Three Mile Island30. USSR: Union of Soviet Socialist Republics

References

Gerwick Jr., B.C., 2007. Construction of Marine and Offshore Structures, 3rd edition.CRC Press, Taylor & Francis Group.

Haug, A.K., Eie, R., Sandvik, K., Kvaerner, A., Aoki, E., 2003. Offshore concrete struc-tures for LNG facilities – new development. In: Offshore Technology Conference,p. 15302.

Hirose, K., 2012. 2011 Fukushima Dai-ichi nuclear power plant accident: summaryof regional radioactive deposition monitoring results. J. Environ. Radioact. 111,13–17.

International Atomic Energy Agency, 2011. Status Report for Advanced NuclearReactor Designs, Report 73.

Korea Hydro & Nuclear Power Co., Ltd., 2008. Preliminary Safety Analysis Report(PSAR), revised vol. 1.

Lapp, C.W., Golay, M.W., 1997. Modular design and construction techniques fornuclear power plants. Nucl. Eng. Des. 172, 327–349.

Lee, K.H., Lee, K.H., Lee, P.S., Jeong, Y.H., Kim, J.K., 2011. A new concept of oceannuclear power plant (ONPP). In: Proceedings of Transactions of the KoreanNuclear Society Autumn Meeting, pp. 863–864.

Ludescher, H., Naess, J., Bjerkeli, L., 2011. Detailed Design of a Gravity-basedStructure for Adriatic Liquefied Natural Gas Terminal. Structural EngineeringInternational, Technical Report, pp. 99–106.

U.S. Nuclear Regulatory Commission, 1977. Regulatory Guide 1.115.Van Wijngaarden, W., Oomen, H., Van der Hoorn, J., 2004. Offshore LNG terminals:

sunk or floating. In: Offshore Technology Conference, p. 16077.Waagaard, K., 2004. Design standard for concrete LNG terminal offshore. In: Offshore

Technology Conference, p. 16207.